Transcript transcription_ translation and protein synthesis REGULAR

Transcription,
Translation &
Protein Synthesis
Protein Synthesis


Protein synthesis is the process in
which a cell makes protein based on the
message contained within its DNA.
However:


DNA is only found in the nucleus
Proteins are only made outside the
nucleus – in the cytoplasm.
Protein Synthesis


How do the many different messages
within the DNA molecule get to the
many ribosomes outside the nucleus?
A molecular cousin of DNA – RNA – is
used to carry these messages.
Ribonucleic Acids (RNA)

There are three types of RNA:
1.
2.
3.
mRNA – carries a message from the DNA to
the ribosome
tRNA – transports amino acids to the mRNA
to make a protein
rRNA – make up ribosomes, which make
protein.
Ribonucleic Acids (RNA)

RNA is almost exactly like DNA, except:
1. RNA has a sugar ribose
DNA has a sugar deoxyribose
2. RNA contains uracil (U)
DNA has thymine (T)
3. RNA molecule is single-stranded
DNA is double-stranded
Ribonucleic Acids (RNA)
Protein Synthesis

Occurs in TWO steps:
Transcription – the genetic information
from a strand of DNA is copied into a
strand of mRNA
2. Translation – the mRNA, with the help
of the ribosome, forms a chain of amino
acids (eventually forming a protein)
1.
The Central Dogma

This order of events is called the
central dogma of molecular biology:
DNA
RNA
P
R
O
T
E
I
N
Step One: Transcription
1.
2.
3.
DNA unzips
Bases pair up: Free nucleotides in the cell
find their complementary bases along the
new strands. What will be different??
New backbone formed: What will be
different??
Step One: Transcription

Watch this simplified animation:

Transcription animation
Step One: Transcription

Try it! What RNA strand will be made
from the following DNA sequence?
TACGCATGACTAGCAAGTCTAACT
AUGCGUACUGAUCGUUCAGAUUGA
Step One: Transcription

Try it! What RNA strand will be made
from the following DNA sequence?
TACGCATGACTAGCAAGTCTAACT
AUGCGUACUGAUCGUUCAGAUUGA
Step 1½: RNA Editing



An mRNA molecule has to be “edited”
because there’s a lot of unnecessary
information that needs to be removed.
An mRNA sequence that does NOT
code for protein is called an intron.
A sequence that is useful in making a
protein is called an exon.
Step 1½: RNA Editing
DNA
transcription
pre-RNA (in nucleus)
exon 1
interon
RNA editing
exon 2
interon
interon
interon
RNA (in cytoplasm)
exon 1
exon 2
exon 3
exon 3
Step Two: Translation
1.
2.
3.
So how do you exactly go about
determining what protein your cells
are going to make?
FIRST, Divide the mRNA sequence into
codons.
Codons are three-base sections of
mRNA:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
3. Translation

Three parts:
1. initiation: start codon (AUG)
2. elongation:
3. termination: stop codon (UAG)
Step Two: Translation

Watch this simplified animation:

Translation Animation
Step Two: Translation

Problem:


There are 20 different amino acids.
There are 4 RNA bases.
A T C G
phe
ile
leu
val
met
pro
ser
ala
thr
his
tyr
asn
gln
asp
lys
cys
glu
arg
trp
gly
Step Two: Translation
You need to figure out what amino
acid matches up with each codon:
2.
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
?
tRNA




A go-getter.
Gets the right amino acids to make the right
protein according to mRNA instructions
It contains anti-codons
EX: UAC – mRNA

AUG – tRNA
Transfer RNA (tRNA)
amino acid
attachment site
methionine
U A C
anticodon
amino acid
The Genetic Code
Step Two: Translation
2.
Since each 3-letter combination
“codes” for an amino acid, you need
to figure out what amino acid matches
up with each codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
met
?
The Genetic Code
Step Two: Translation
2.
Since each 3-letter combination
“codes” for an amino acid, you need
to figure out what amino acid matches
up with each codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
met
arg
thr
asp
arg
ser
asp
???
Step Two: Translation
2.
Since each 3-letter combination
“codes” for an amino acid, you need
to figure out what amino acid matches
up with each codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
met
met
thr
asp
arg
ser
asp
STOP
RECAP:
1.
2.
3.
DNA is transcribed
into mRNA in the
nucleus.
The mRNA leaves the
nucleus and enters the
cytoplasm.
The protein is
translated from the
mRNA sequence using
tRNA and amino acids.